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348

LIGHTING OILS

sulphuric acid (D 1-53) and note made if the latter becomes yellow or brown.
If any appreciable coloration occurs, it is desirable to ascertain if any marked
rise of temperature takes place.

3.  Determination of the Sulphur.—This is usually done only with
oils having a penetrating and unpleasant odour.    The simplest method is
that of Heussler and Engler,1 this consisting in burning the petroleum in
a suitable lamp, the chimney of which is joined to a bent tube dipping into
20 c.c. of 5% potassium hydroxide solution made just yellow by bromine
and then left in the air to decolorise ; the absorption vessel communicates
with a pump.    The lamp charged with the oil is weighed and lighted, the
tube fitted and the suction adjusted so that the combustion is complete and
regular.   The sulphurous anhydride produced is absorbed and transformed
into sulphuric acid by the alkaline bromine solution.    After 10-12 grams
of the oil are burnt, the flame is extinguished, a little more air drawn through,
the lamp again weighed and the sulphuric acid determined as barium sul-
phate.   The caustic potash used and also the air must, of course, be free
from sulphur products.

The sulphur may also be determined by the Mahler calorimetric bomb (see
Crude Petroleum, Chemical Tests, 3).

4.  Distinction between Petroleums from Different Localities.—

This is based mainly on the following tests :

(a) SPECIFIC GRAVITY. This is usually 0-780-0-805 for American and
0-820-0-825 for Russian lighting oils.

A better criterion than the specific gravity is furnished by the specific gravities
of the fractions obtained on distillation, these differing by about 0-04 for identical
boiling points. Thus, the fractions of an American and a Russian petroleum
distilling between 230° and 250° have the respective densities 0-798 and 0-841,
and the fractions between 250° and 270° the densities 0-809 an-d 0-850.

(6) TREATMENT WITH BROMINE. 2 or 3 c.c. of American petroleum
are not coloured when treated with a drop of bromine, whereas other
petroleums become coloured under these conditions.

(c) SOLUBILITY IN A MIXTURE OF CHLOROFORM AND ALCOHOL. Riche
and Halphen 2 have suggested a method based on the different solubilities,
in a mixture of chloroform and aqueous alcohol, of fractions of equal specific
gravities from American and Russian petroleums. It is carried out as
follows : Several successive fractions of the oil are separated by distillation
and the specific gravity of each of them determined at 15°. The volume
of a mixture in equal volumes of pure anhydrous chloroform and 92-8%
alcohol necessary, when run in slowly from a burette with continual shaking,
to remove the turbidity produced, is then determined. For the lighter
fractions (which have about the same compositions with Russian and
American petroleums), the solubility is about the same for the same specific
gravities, but for fractions with specific gravities above 0-760, the difference
in solubility continuaUy increases. Thus, the corresponding fractions of

1 Chem. Zeit., 1896, p. 197.

,2 Journ. de Pharm. et Chim., 1894, XXX, p. 289 ; Rossi: Ann. Labor. Chim. Gabelle,
1900, IV, p. 379. substances in 20 c.c. of the oil.